using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    public class Expression {

        public Expression Left;

        public int[] LeftVal;

        public Expression Right;

        public int[] RightVal;

        public string Operator;

        public int[] Evaluate() {

            switch (Operator) {

                case "+":

                    return Left.Evaluate() + RightVal.Evaluate();

                case "-":

                    return Left.Evaluate() - RightVal.Evaluate();

                case "*":

                    return Left.Evaluate() * RightVal.Evaluate();

                case "/":

                    return LeaveUntilLast;

                case null:

                    //Handle Base Case

                    if (Left == null) {

                        return RightVal;

                    } else { //(Right== null)

                        return LeftVal;

                    }

                default:

                    return null;

            }

​

        }

    }

}